As with all AWS services, you pay for what you use. There is no up-front fee; users simply pay for the storage they use, said AWS evangelist Jeff Barr in a blog post.

"With Glacier, you can store any amount of data with high durability at a cost that will allow you to get rid of your tape libraries and robots and all the operational complexity and overhead that have been part and parcel of data archiving for decades," Barr said.

Glacier is targeted at "cold" data-data that organizations typically will not seek to retrieve for some time. "You don't have to worry about capacity planning and you will never run out of storage space," Barr said. "Glacier removes the problems associated with under or over-provisioning archival storage, maintaining geographically distinct facilities and verifying hardware or data integrity, irrespective of the length of your retention periods."

Barr said Glacier plays off the success of Amazon's Simple Storage Service (S3), which AWS launched in 2006 and now stores over 1 trillion objects. "Glacier builds on S3's reputation for durability and dependability with a new access model that was designed to be able to allow us to offer archival storage to you at an extremely low cost," he said.

However, there are differences between S3 and Glacier. For one, S3 is designed for rapid data retrieval and Glacier is not. "Retrieval requests are priced differently, too," Barr said. "You can retrieve up to 5% of your average monthly storage, pro-rated daily, for free each month. Beyond that, you are charged a retrieval fee starting at $0.01 per gigabyte (see the pricing page for details). So for data that you'll need to retrieve in greater volume more frequently, S3 may be a more cost-effective service."

Glacier sounds like a great deal, and quite likely is. However, Wired Enterprise has examined the issue of data retrieval with Glacier and whether the costs there might become prohibitive.

According to Wired:

Because the service is designed for long-term archival needs, not active use, it's understandable that the fees for retrieval will be high in comparison to the fees for storage to discourage the use of Glacier for general-purpose storage. It will also take three to five hours to prepare an archive for downloading, which will also deter misuse of the service. Presumably, Amazon powers off the hardware until it's needed.

But the retrieval fees are confusing. According to Amazon's pricing chart, you can request up to 5 percent of the data stored in Glacier for free each month, but it's prorated by the day. The FAQ explains: "If on a given day you have 12 terabytes of data stored in Glacier, you can retrieve up to 20.5 gigabytes of data for free that day (12 terabytes x 5% / 30 days = 20.5 gigabytes, assuming it is a 30-day month)." Elsewhere in the FAQ it explains that this is about 0.17 percent a day ("5% / 30 days = 0.17% per day").